Within the field of chip removing or cutting machining of blanks of metal, a continuous development is going on with the purpose of making more effective not only the capacity of the tools to carry out the machining in a fast and accurate way, but also the manufacture of the different parts of the tools in the form of basic bodies (e.g. holders) and replaceable cutting inserts. A trend of development is to improve the machining results in respect of the precision and surface finish, which requires that the active cutting edge of the cutting insert obtains an exact, predetermined space position in relation to the basic body. Another trend is to reduce the costs of the manufacture of the tools. This has, among other things, led to the cutting inserts being made from cemented carbide, which are most commonly occurring on the market, already in connection with the compression-moulding and sintering having obtained a better and better dimensional accuracy. In order to obtain a good precision of the cutting inserts, previously it was necessary to subject the inserts to expensive grinding operations, but with the improved compression-moulding and sintering technique, it has become possible to use direct-pressed, i.e., unground, cutting inserts in more and more applications. However, the development has not progressed further than that the tool designer still has to allow for a dimensional variation of the order of ±0.5% of the nominal dimensions of the cutting insert. This means that the active edge of the cutting insert very well may end up in the desired position when the result of the insert manufacture is good, but when the result is poorer (so far that the cutting insert has swollen and become longer, or shrunk and become shorter than intended), the position of the cutting edge in relation to the basic body may deviate to such a high extent from the desired position that the machining precision will become less good.
Recently, tools have been developed, the interfaces of which between the basic body and the cutting insert are formed with connecting surfaces that individually include male-like as well as female-like engagement structures engaging each other. Originally, the connecting surfaces included so-called serration connecting surfaces, of the type that includes a plurality of parallel, male-like ridges and female-like grooves, the ridges of which in one of the connecting surfaces engage the grooves of the other connecting surface, and vice versa. In the next development step, the interfaces were refined by the fact that certain ridges were orientated at right or other angles to the other ridges, often in combination with the number of ridges being reduced. However, common to previously known interfaces is still that the male-like engagement structures are more or less elongate, straight ridges having inclined flanks, which provide for the positioning of the cutting insert as well as the transfer of force from the cutting insert to the basic body, by the fact that the flanks of the ridges should have a good contact along the entire length thereof, at the same time as the ridges must not touch the bottom of the appurtenant grooves.
Within the art of chip removing machining, there is a difference between theory and practice. Thus, in theory, it is fairly simple to construct interfaces that have optimal properties in respect of stably fixing the cutting insert and the active cutting edge thereof in an exact predetermined position in relation to the basic body, and ensuring good absorption of the various forces that act on the cutting insert during operation. However, in practice, the stability and position of the cutting insert are affected by a number of unforeseeable factors, one of the most difficult to master of which is the varying result of the manufacture of the cutting inserts. As long as the result gives a good, nominal dimensional accuracy, the intended and calculated surface or line contact, among other things, is obtained between the flanks of the ridges and of the grooves along the entire length of the flanks, but when even moderate form defects arise, there is a risk that the contact between the flanks is reduced to point contacts or partial line contact. This may in turn result in the cutting insert, initially as well as during operation, being positioned incorrectly in relation to the basic body (by so-called overdetermination), and that the transfer of force between the cutting insert and the basic body becomes inferior.
As an example of prior art, reference is made to U.S. Pat. No. 6,146,061, which discloses a cutting tool, the replaceable cutting insert of which is connected to a tool basic body via an interface, the two co-operating connecting surfaces of which include mutually intersecting serrations in the form of long narrow male and female members. More precisely, two first, mutually parallel chutes are formed in the connecting surface of the basic body, which are delimited by diverging side-flank surfaces, and which are intersected by a second transverse chute extending perpendicularly to the first chutes and likewise is delimited by diverging flank surfaces. The connecting surface of the cutting insert includes, on one hand, two first, longitudinal and mutually parallel male members in the form of ridges having converging side-flank surfaces, and on the other hand two male members or ridges projecting at right angles from the external side-flank surfaces of the first ridges, the width of which is somewhat smaller than the width of the transverse chute. When the cutting insert is applied with the connecting surface thereof in engagement with the connecting surface of the basic body, the cutting insert is guided axially by the fact that the two side-flank surfaces of the central ridges abut against the two side-flank surfaces of the central chutes, i.e., the two ridges have flank contact with the two chutes without touching the bottom of the same. In order to determine the axial position of the cutting insert along the length extension of the central chutes, rear flank surfaces on the two projecting, transverse ridges are pressed against the rear flank surfaces in the transverse chute, more precisely by an elastically resilient screw used to finally fix the cutting insert.
In theory, the above-mentioned way to fix the cutting insert is attractive, but in practice, the cutting insert may come to be mis-positioned. Such a mis-positioning is particularly awkward if the cutting insert is indexable and includes two or several active cutting edges situated along corners of the cutting insert. In particular, if form defects arise in the manufacture of the cutting inserts, e.g., so far that one of the ridges shrinks or swells in relation to the other, the cutting insert will assume a “tilted” or inclined position in the connecting surface of the basic body. Another disadvantage with the known tool is that the connecting surface of the basic body includes a comparatively large number of flank surfaces, which already, as a consequence of the large number thereof, complicate the manufacture of the basic body and increases the risk of sources of error.
The present invention aims at overcoming the above-mentioned problems by providing a cutting tool having an improved interface between the basic body of the tool and the individual cutting insert. Therefore, an object of the invention is to provide a tool having an interface that, on one hand, can fix the cutting insert stably in such a way that the active cutting edge of the cutting insert is reliably located in a correct, non-overdetermined position in relation to the basic body, and on the other hand can absorb considerable cutting forces in the area where the need for stability is the greatest, viz. in the immediate vicinity of the corner of the cutting insert that includes the active cutting edge.
Another object of the invention is to provide an interface that not only locates the cutting insert in the desired way initially in connection with the mounting, but also can retain the stable fixation of the cutting insert under the severe stresses encountered by the cutting insert during the chip removing machining. In addition to affording an improved absorption of such forces that act in the direction from above and down into the cutting insert, the interface should therefore prevent the cutting insert from becoming translated and rotated, respectively, in relation to the basic body.
Yet another object of the invention is to provide an interface that ensures the desired properties in respect of the positional accuracy and the force-transfer capacity, without the manufacture of the basic body and cutting insert of the tool being made more difficult or more expensive. In particular, the cutting insert should, if required, be possible to be manufactured by direct pressing, i.e., without needing to be subjected to expensive grinding operations.
Still another object of the invention is to provide a tool, the cutting inserts of which can be fixed in an exactly predetermined end position without the help of any resilient screw. Furthermore, the connecting surface of the basic body should be easy to manufacture and contain as few limiting surfaces as possible.
Still another object of the invention is to provide a cutting tool, the cutting inserts of which can be indexed in two or more positions.